The present invention relates to an inflatable seat belt apparatus, more particularly to an inflatable seat belt, wherein a webbing of a seat belt apparatus to restrain an occupant has an inflatable portion formed in an envelope shape which is usually maintained in a band shape and is inflated in a predetermined shape by high temperature gas spouted from gas generating means at a crash. In the invention, the inflatable seat belt can be inspected automatically whenever the occupant wears the seat belt as to whether or not the inflatable portion is damaged.
Presently, a seat belt apparatus is necessary for a vehicle or the like as an apparatus for securing an occupant's body, which restrains the occupant from sudden movement by an deceleration and an impact occurred at a crash.
Such a seat belt apparatus comprises a normal webbing ("a webbing" is used hereinafter as a woven belt made of a normal fabric which has approximately a 50 mm width and is provided by Japanese Industrial Standard in this specification), a retractor (hereinafter, ELR: Emergency Locking Retractor is denoted instead of the retractor), a buckle, a tongue, an anchor and so on. The ELR winds the webbing by a spring force and locks the webbing from withdrawing only at a crash so as to restrain the occupant. The buckle is mounted to a suitable position so that the webbing fits the occupant's body well.
Conventionally, the seat belt apparatus locks the webbing from withdrawing by the function of ELR at a crash to restrain the occupant from forward movement.
For improvement in the efficiency of restraining the occupant, each of U.S. Pat. Nos. 3,841,645, 3,865,398, and 3,866,940 discloses a seat belt apparatus in which the webbing has a portion formed in an envelope shape made of a fabric. The webbing is folded like bellows and then provided with weak adhesive so as to usually maintain in a band shape, or the folded portion is maintained in the band shape by fastening means such as a fastener, so that at a crash, the portion formed in an envelope shape is inflated and deployed by spouted gas from a gas generator connected to the webbing.
According to the seat belt apparatus having the inflatable portion formed in an envelope shape (hereinafter, called "an inflatable seat belt apparatus"), the force applied to the occupant can be distributed over the range wider than the conventional webbing so as to decrease the stress applied to the occupant and a higher safety efficiency can be provided.
The inflatable seat belt apparatus can be effective even for a rear seat. For mounting an air bag apparatus for an occupant on the rear seat, the air bag apparatus is generally mounted on the rear side of the back portion of the front seat. It is necessary that the front seat structure has a high rigidity for suitably operating the air bag apparatus for the rear seat to efficiently restrain and secure the occupant. Therefore, it is difficult to have the reclining function to the front seat if the air bag apparatus is mounted on the rear side of the back portion of the front seat. Therefore, the inflatable seat belt apparatus is quite effective for the rear seat because the inflatable seat belt apparatus can be independently mounted on the rear seat and has no restriction such as the air bag apparatus.
In the inflatable seat belt apparatus mentioned above, the gas generator operates according to an operation signal from a sensing unit such as an acceleration sensor sensing an impact at a crash and the enveloped shaped inflatable portion is then substantially instantaneously inflated and deployed in a predetermined form.
Recently, most of the gas generator (hereinafter, called "inflator") is a device for instantaneously generating gas by use of a rapid combustion of filled up compound.
The inflator receives, first, the operational signal from the acceleration sensor at a crash to act as a trigger for the electrical squib. An ignitor is actuated by the electrical squib to burn a propellant so as to rapidly generate gas.
The propellant may be sodium azide (NaN.sub.3) which is well known as a propellant and generates nitrogen gas by combustion.
In case of the conventional inflatable seat belt apparatus in which the thick fabric is folded, the inside of the fabric is coated with silicone rubber to provide higher airtightness for the envelope shaped portion and the inflator is provided with a simple filter for cooling an inside thereof to lower the temperature of the introduction gas so that the high temperature gas from the inflator is directly introduced into the envelope shaped portion.
The applicant has already disclosed an invention of the inflatable seat belt apparatus in which the envelope shaped portion is formed from a knitted textile and has an inflatable unit having a rubber tube inside thereof. Furthermore, the applicant has already disclosed an invention of the inflatable seat belt apparatus in which the envelope shaped portion is formed from a fabric having wefts which expand enough and has an inflatable unit of rubber tube inside thereof (Japanese Patent Application No. 210353/1992, No. 210355/1992, No. 78623/1993, No. 78624/1993).
According to the above mentioned inventions, when the occupant usually wears the inflatable seat belt apparatus, the envelope shaped portion is maintained in a thin band shape as compared with the conventional inflatable seat belt apparatus in which the thick fabric is folded. Furthermore, in an emergency, the envelope shaped portion can be quickly inflated and deployed without fail.
FIG. 1(a) illustrates an example of the inflatable seat belt apparatus in which a shoulder belt having a pipe portion is formed of a knitted textile and has an inflatable unit of rubber tube inside thereof.
In this figure, numeral 101 designates a tongue. The tongue 101 has a gas inlet 104 as an inlet for introducing the gas into a rubber tube 103 arranged in the belt 102. The gas inlet 104 is coupled to a gas outlet 106a of gas generating means (inflator) 106 situated inside a buckle 105 when the tongue 101 is engaged with the buckle 105 for fixing a belt end 102a to the vehicle body.
FIG. 1(b) exemplifies a state of a belt 102 inflated and deployed in a predetermined shape. The propellant in the inflator 106 is burned to generate reaction gas, and the gas is introduced into the rubber tube 103 of the belt 102 through the gas inlet 104, so that the belt 102 is inflated and deployed in the predetermined shape.
As the gas is rapidly introduced into the rubber tube 103, the rubber tube is inflated as shown in the FIG. 1 (b), wherein the shape of the whole inflatable portion is controlled by a knitted textile structure 107 formed in an envelope shape which covers the rubber tube 103. Therefore, the inflatable portion becomes a spindle shape. Because the area of the belt portion touching the chest and the like of the occupant is increased, an impact applied to the occupant is softened.
Because the inflatable portion formed in an envelope shape is radially increased, the length of the belt in a longitudinal direction is shortened by .DELTA.L. Therefore, the inflatable seat belt apparatus has a function as a pre-tensioner by which the occupant is more effectively ensured.
In the inflatable seat belt apparatus of this kind, the gas spouted from the inflator is introduced into the tube with a high temperature and high pressure condition.
FIG. 2 is a temperature distribution diagram exemplifying a result of measuring the temperature distribution within the tube at this stage. The figure also shows the inflatable portion in a inflated condition below the diagram to indicate the relative position.
At this stage, the inside of the tube has a highest temperature at a tongue portion near the gas inlet as shown in FIG. 2. The highest temperature tends to be approximately 1,300.degree. C. At each point in the tube in the longitudinal direction L, respective temperatures appear with introduction of the gas as shown by the dotted lines. The solid line shows a curve tracing the respective temperatures at each point.
The gas generated by the combustion in the inflator is quite high temperature. However, because the temperature drops along the longitudinal direction, the tube works efficiently if only it can withstand the high temperature for a very short period.
A silicone rubber of a heat resistance has been adapted to the tube for receiving the high temperature gas to withstand the high temperature in the tube.
However, in the above mentioned inflatable seat belt apparatus, it is thought that the tube is damaged for some reason.
Even if the tube is damaged, the inflatable seat belt apparatus can work as a normal seat belt apparatus because the webbing extends over the whole seat belt. However, in case of inflating the belt portion by introducing the reaction gas by acting the inflator, the gas is flown out of the tube form the damaged portion of the tube, so that the function of the inflatable seat belt apparatus may not effectively work. Therefore, it is preferable that the inflatable. seat belt apparatus can be inspected whether or not the inflatable portion such as the tube is damaged.
In this case, the driver brings a gas leak detector in the vehicle and introduces gas for detecting a gas leak into the inflatable portion by using the tongue as an inlet to detect the gas leak. This work is too heavy burden for the driver's every day check up, so that the driver tends not to do it.